Information on the intense thunderstorms in the Alcázar de San Juan (Ciudad Real) area on 23 May 2007

Information on the intense thunderstorms in the Alcázar de San Juan (Ciudad Real) area on 23 May 2007

29

Published

29 May 2007

Press Release Number:

N/A

News from the Spanish National Insititute of Meteorology

During the afternoon of 23 May 2007, intense thunderstorms affected the Alcázar de San Juan (Ciudad Real) area producing heavy precipitation which in some places exceeded 200litres per square metre. The general atmospheric situation was marked by the presence of a cold storm in the upper air over the NE of the Spanish peninsula and a warm, humid flow in the low levels.(28/05/07)

Throughout the second half of the day, convective activity increased over the southern plateau causing several storms which moved SE-NE with the prevailing wind. In the early hours of the afternoon, the radar watch images for the central zone showed that one of them was developing more than the others and in spectacular fashion. Its uniqueness was accentuated by the fact that its displacement gradually deviated from the mean wind and hence from the other storms in the area. At the same time, it became very large and remained almost stationary in the area NE of Ciudad Real and the border with the province of Toledo for several hours.

In meteorology, such thunderstorms are called “supercells”, which are highly organized convective structures characterized by strong rotating updraughts and an embedded mesocyclone. Occasionally, as occurred in this case, supercells produce torrential rainfall. Their tracks are usually isolated from those of the other storms in the vicinity. In this case, the supercell remained practically stationary in the area of Alcázar de San Juan, and caused copious amounts of precipitation.

The provisional precipitation data available so far show that in Alameda de Cervera (Ciudad Real) 240 mm fell between 8 a.m. on 23 and 8 a.m. on 24 May 2007, which is more than twice the estimated value for precipitation with a 50-year return period.

Estimated accumulated precipitation obtained from the Madrid radar data for the period 12UTC-18UTC (2-8 p.m. local time) on 23 May. The area with the most precipitation produced by the supercell that remained quasi-stationary overhead can be clearly seen.